.loop(@counter) when (@counter > 0){
    .col-@{counter}{    // 变量作为选择器时，
        width: (@counter * 5%);
    }
    .loop((@counter - 1));
}
.loop(20);
.title { 
    text-align: center; 
    height: 30px; 
    line-height: 30px; 
    font-size: 16px;
}
#x-spreadsheet-demo { 
    top: 0px;
    left: 100px; 
    bottom: 0px; 
    width:  calc(100% - 100px);
    position: absolute; 
    border: 1px solid #D6D6D6; 
    margin: 0px auto; 
    overflow: hidden;
    box-sizing: border-box
}
.tools {
    position: absolute; 
    bottom: 0px;
    left: 0px; 
    width: 100px; 
    padding: 0px 0px; 
    margin: 0px 0px;top: 0px;
    .group { 
        position: relative; 
        font-size:  0px;
        .btn { 
            display: inline-block; 
            padding: 0px 0px; 
            margin: 0px 0px; 
            box-sizing: border-box;
        }
    }
}
